Improve the structure of the static directory

[mariusmucenicu]

As the project expands there will be multiple css & javascript files as well as other files, such as images and svgs.

Right now, they are all bundled together under the same directory, which is static/.

These need to be further split per logical unit, as follows:

• all the css files need to go under /static/css/
• all the js files need to go under /static/js/

This can be further split down the line per sub-logical unit, such as

• all external css files can go under /static/css/frameworks/ and so on..

Also don't forget to update .gitignore